If the cookies start to harden up too quickly, just pop them back in the oven for a few seconds to make them pliable again.
The most important step for the cannoli filling is draining the ricotta to remove as much moisture as possible, which will keep the filling thick and easy to pipe, and prevent the florentines from losing their crispness.
You can make the shells and the filling ahead of time, then pipe in the filling an hour or so before serving.